1. Field of the Invention
This invention relates to improvements in modular plastic conveyor belts and modules therefore. In particular, this invention concerns a unique pivot rod retention arrangement and unique link end shapes and stiffening construction for the individual modules of the belt.
2. Prior Art
The basic concept of modular conveyor belts in which there are a plurality of modules having interfitting link ends which are held together by pivot rods extending through holes in the link ends has been known since the nineteenth century as shown by the German Patent No. 113,619, Mallard, 1899.
In the 1970's, various modular conveyor belts were molded of plastic and included arrangements for stiffening the modules intermediate the link ends. See for example, U.S. Pat. No., 3,870,141, Lapeyre, et. al., 1975.
The retention of the pivot is an important feature of the modular plastic conveyor belts. Rod retention can be accomplished by enlarging the heads of the pivot rods but such would not allow for disassembly without destroying the rod head. It is important to be able to remove the pivot rods from the assembled plastic conveyor belt while the conveyor belt is installed on location for repairs as may be required. Therefore, it is important to have a rod-retention arrangement which will allow for easy removal of the pivot rod for reassembly but will retain the rod in position during operation. U.S. Pat. No. 3,939,964, Poerink, 1976 shows one such rod retention arrangement in which pins are inserted into transverse bores which intersect the pivot rod holes outside the ends of the pivot rods, i.e. the bores and pins are in the outermost link end of the end modules. This has an advantage of not positively interlocking with the pivot rods as the pivot rods may expand or contract at different rates than the remainder of the assembly.
A similar approach to rod retention is shown in U.S. Pat. No. 5,024,321, Lapeyre, 1991. In this patent a module has a slot extending completely through a thickened outermost link end for the insertion of a bifurcated retaining pin which, when inserted blocks the pivot pin hole. However, the pin must be inserted from the top surface of the conveyor and for removal a screwdriver or similar instrument must be used to push the pin out from the top or bottom of the conveyor. Thus, access must be had to both the top and bottom of the outermost conveyor belt link in order to remove the pin and hence remove the rod.
A further approach to rod retention is shown in U.S. Pat. No. 4,893,710, Bailey et al., 1990, wherein a blocking member of a unique molded shape fits in a complementary shaped slot. The blocking member is also flush with the top of the conveyor. While this construction is quite successful, it does have a disadvantage in that the blocking members (similar to the pins of the prior art mentioned above) are small and can easily be lost or misplaced. Furthermore (similar to the other prior art mentioned above) the blocking members must be removed via access from the top and bottom surfaces of the conveyor belt.
Another approach to rod retention is disclosed in U.S. Pat. No. 5,000,312, Damkjaer, 1991. In this patent the links or modules are not bricklayed, but instead are assembled so that chains of identical modules are side by side. The outer link ends of all modules are thicker than the others to accommodate locking dowels which may be inserted into a notch. These locking dowels have the same disadvantages of being easily lost or misplaced and having to be inserted inconveniently.
Because all of the blocking of exclusive movement of pivot rods by pins, dowels, abutments, blocking members or the like of the prior art are loose and can be removed, a problem is created when repairs are required in the field. If a pivot rod blocking member is removed and misplaced or lost then time for repairs will be lost. Furthermore, in the prior art, in order to remove the pivot rod, the blocking member itself must be removed and access must be had to the top and bottom of the conveyor belt edges in order to remove the blocking member. Thus, there is a need in the art for a blocking member which is captured i the module end link and which can be moved to and from blocking position, i.e. one position to block the movement of the pivot rod out of the hole and the another position to unblock the pivot rod hole to allow removal of the pivot rod for repair or disassembly.
There if also need in the prior art for conveyor modules in which there are relatively wide link ends to accommodate the teeth of a driving sprocket and relatively narrow link ends to provide as many pivot rod shear planes as possible in the same module. This obviously involves link ends of varying widths. And while link ends of varying widths have been known in the art, see e.g. U.S. Pat. No. 3,726,569, Maglio, 1973, U.S. Pat. No. 4,893,710 and German Patent 113,669 mentioned above, none are directed to driving at the link end via a wide link end and providing a plurality of narrow link ends for increased pivot rod shear planes.